The field of the invention is electrical relays which employ magnetically responsive sealed switches, and more particularly, relays such as that disclosed in U.S. Pat. No. 3,605,049 issued on Sept. 14, 1971, and entitled "Sealed Contact Relay".
Such sealed contact relays are known for their high reliability, speed of operation and suitability for use in adverse operating conditions. They are typically interconnected with other similar relays and mounted within a common cabinet to form a control system for industrial equipment such as molding machines, metalworking machines and transfer lines.
Control systems formed from sealed contact relays must often perform timing functions. Timing modules are offered by a number of manufacturers which may be employed either as separate units in the control system or which may be mounted to a conventional relay as an optional feature. Timers must be reliable, rugged, compact and accurate for use in relay control systems and they have heretofore employed either mechanical timer mechanisms or analog electrical circuits such as that disclosed in U.S. Pat. No. 3,249,771, issued on May 3, 1966, and entitled "Stabilized Timing Circuit". Mechanical timers include expensive components and analog electrical timing circuits must be individually calibrated during manufacture which adds considerably to their cost.